The retinoic acid receptor RARbeta is highly expressed in the striatum of the ventral telencephalon. We studied the expression pattern of different RARbeta isoforms in the developing mouse striatum by in situ hybridization. We found a differential ontogeny of RARbeta2 and RARbeta1/3 in embryonic day (E) 13.5 lateral ganglionic eminence (striatal primordium). RARbeta2 mRNA was detected primarily in the rostral and ventromedial domains, whereas RARbeta1/3 mRNAs were enriched in the caudal and dorsolateral domains. Notably, by E16.5, a prominent decreasing gradient of RARbeta2 mRNA was present in the developing striatum along the rostrocaudal axis, i.e., RARbeta2 was expressed at higher levels in the rostral than the caudal striatum. No such gradient was found for RARbeta1/3 and RARbeta3 mRNAs. The rostrocaudal RARbeta2 gradient gradually disappeared postnatally and was absent in the adult striatum. The differential expression pattern of RARbeta isoforms in the developing striatum may provide an anatomical basis for differential gene regulation by RARbeta signaling.